As shown in FIG. 1, a prior art electric connector is used to electrically connect a memory module and the mother board of a computer. This prior art electric connector substantially includes a long insulating housing 10, with a longitudinally extended central groove 12 arranged on the central portion of the housing 10. A plurality of paired terminal holes 14 spaced by the central groove are arranged on the two transverse opposite side walls of the housing 10 along the longitudinal length of the housing. Into each of the terminal holes 14 is inserted a terminal 16. When the edge of a circuit board 20 is inserted into the central groove 12, the terminal within the terminal hole with electrically connect with the circuit track 22 of the edge of the circuit board.
The circuit board 20 must be steadily inserted into the central groove 12 so that a steady electric connection is achieved, and the insertion and pulling of the circuit board 20 can be performed easily. Generally each of the longitudinal distal ends of the insulating housing 10 has a latch structure 30. As shown in FIG. 1, the latch structure 30 is typically installed on the installing seats 18 of the two ends of the housing 10. The latch structure 30 typically includes a head 32, a pivotal arm 34, a pivotal axial portion 36 and an ejecting arm 38. The latch structure 30 shown in the right side of FIG. 1 has been installed on the installing seat 18 and is in a releasing position, while the latch structure 30 of the left side of FIG. 1 has not been installed in the installing seat. In assembling, the latch structure 30 is pressed into an opening 181 formed on the installing seat 18 by a press-fit manner so that the pivotal axial portion 36 may be inserted into the pivotal hole 19 below the opening 181. Thus, the latch structure 30 within the opening 181 may pivotally rotate between a locking position and a releasing position.
When a circuit board 20 has been inserted into the central groove 12, the lower portion of the edge of the circuit board will push against the ejecting arm 38 of the latch structure 30, thus the latch structure 30 will rotate inwards in to the locking position. In the locking position, the forward projected buckling portion 321 of the head 32 of the latch structure 30 will buckle with the concave mouth 24 on the side of the circuit board 20. Thereby, the circuit board may be steadily fixed in the groove of the connector. When the circuit board is required to be released from the central groove 12, as shown in FIG. 1, the thumb will press downwards the upper surface 322 of the head 32. Then a downward horizontal force will cause the latch structure 30 to rotate outwards to a releasing position. During rotating, the ejecting arm 38 will eject the circuit board upwards. The prior art electric connector may refer to U.S. Pat. Nos. 5,470,240, 5,211,568, 5,389,000, 5,074,800, 5,302,133, and 4,973,255, and Taiwan Patent Nos. 84200526,83213346, 84218006,85215054, and 84212006.
In practice, the above prior art latch structure 30 of an electric connector has many problems. At first, when an unskilled user requires to release this circuit board, he (or she) must use a relatively large force to press downwards on the upper surface 322 of the head 32. Then this downward rotation force causes the head to rotate outwards in the longitudinal direction (now the circuit board is still located in the central groove 12, and the terminal 16 still retains a relative holding force). However, once the circuit board has been ejected upwards to be released from the holding force (i.e. the latch structure attains a releasing position), the downward rotation force generally can not be stopped in time and still presses downwards. Therefore, the pivotal axial portion 34 will break near the pivotal axial portion 36.
Next, the prior art "pressed rotation" type latch structure needs much force in operation, since most of the user's force is applied downwards, only a small horizontal component of the force is used to effectively rotate the latch structure. Besides, since the usable space in the mother board of current computers is more and more compact, such kind of "pressed rotation" type latch structure is inconvenient in operation in some environments. Moreover, effective protection has not bee provided in a breakable portion of a prior art latch structure (the portion adjacent to the pivotally axial portion), thus, such kind of "pressed rotation" type latch structure often breaks in use.
Furthermore, as shown in FIG. 7, an electric connector for electrically connecting a circuit board (such as RAM modular) and the mother board of a computer is shown. This kind of electric connector typically includes a long insulating housing 10B the central portion of which has a longitudinally extending central groove 12B. A plurality of paired terminal holes 14B spaced by the central groove 12B are arranged on the two transverse opposite side walls 10B of the housing 10B along the longitudinal length of the housing 10B (as shown in the direction indicated by the arrow L of FIG. 7). Into each of the terminal holes 14B is inserted a terminal 20B. When the edge of a circuit board (not shown) is inserted into the central groove 12B, the terminals 20B within the terminal holes will electrically connect with the circuit track on the edge of the circuit board.
Generally, this kind of electric connector has two types of terminals (i.e. the first terminal 20B and the second terminal 20'B according to the present invention as shown in FIG. 7, or the first terminal 50B and the second terminal 50'B according to the prior art as shown in FIG. 10A). In general, these two types of terminals are alternatively arranged in and inserted into the terminal holes (for example, the odd number holes are used by first terminals, while the even number holes are used by second terminals). The terminal holes with respect to the opposite two side walls 11B are inserted by first and second terminals, respectively (for example, if the first terminal hole of one side wall is inserted by a first terminal, then the first terminal hole of another side is inserted by a second terminal).
Referring to FIGS. 10A and 10B, a prior art terminal structure of this kind of electric connector is shown. As shown in the figure, in order that the circuit board inserted by the terminals 50B, 50'B may attain a steady electric connection, an elastic contact portion 505B having a bent shape is designed in the terminals so that a constant contact force is formed between the terminal and the circuit board, and to prevent the terminal from being obliquely inserted into the terminal hole to cause an unsteady contact between the terminal and the circuit board. In this general design, the terminal is held in the terminal hole by a pre-stress. For example, in FIG. 10A, the distal end of the curved elastic contact portion 505B presses against the rib 601B above the insulating housing by a pre-stress. In the following description and claims, the word "pre-stress" means that when the terminal is inserted in a terminal hole, a stress is applied on the terminal, and in general, the stress is provided by the elasticity of the terminal itself.
Although, the prior art terminal may have a steady electrical connection with a circuit board, in practical use, it has some potential defects. As shown in FIG. 10B, when the edge of the circuit board 70B is inserted into the central groove of a connector, the edge may press downwards the elastic contact portion of the terminal 50B directly so that the terminal will be buckled. Once one of a plurality (for example, 168) of terminals of the electric connector is buckled, then the whole electric connector will not work.
Moreover, since the prior art electric connector has not provided any device for tightly fixing the terminal within the terminal hole, the electric connector very probable will be buckled due to the shift of the terminal.